Gas or vapor discharge tube



' May 29, 1956 A. A. HURX ,7 ,3

GAS OR VAPOR DISCHARGE TUBE Filed Dec. 18. 1952 INVENTOR. Apzemusmozvlusflm w fla .internal diameter of about 3.6 cms.

United States Patent GAS 0R VAPOR DISCHARGE TUBE Adrianus Antonius Hurx, Eindhoven, Netherlands, as-

signor to Hartford National Bank and Trust Company, Hartford, Conn., as trustee Application December 18, 1952, Serial No. 326,628

Claims priority, application Netherlands January 15, 1952 3 Claims. (Cl. 313-197) This invention relates to gas or vapor discharge tubes, more particularly, to discharge tubes coated internally with a layer of luminescent substances, the so-called fluorescent lamps.

Conventional fluorescent lamps have been provided with a conductive strip on the luminescent layer to facilitate ignition of the lamp, the strip being electrically connected to one of the activated main electrodes inside the discharge space by means of a short metal tape. This connection between the conductive strip and the metal tape is usually effected by means of an adhesive substance applied to the metal tape, which substance becomes liquid when the electrode system is sealed to the end of the tubular discharge vessel thereby establishing a strong contact between tape and strip during subsequent cooling. However, this construction suffers from the drawback that the tubes do not always ignite which probably results from the adhesive interfering with the electrical connection between the tape and the conductive strip.

The main object of the invention is to improve the ignition of a fluorescent lamp of the foregoing type.

According to the invention, in a gas or vapor discharge lamp which is provided internally with a conductive strip electrically connected to one of the main electrodes of the lamp by means of a short metal tape, the end of the metal tape connected to the conductive strip is provided with at least two strip portions alongside one another, one of the strip portions being in direct electrical contact with the conductive strip, while the other strip portion serves to establish a rigid mechanical joint between the conductive strip and the tape. With this construction, it has been found that satisfactory ignition of the discharge tube is assured.

In a preferred embodiment of the invention, the metal tape which is preferably ferro-chromium, is provided at an end thereof with three adjacent strip portions, of which only the central portion is in direct electrical contact with the conductive strip, the other two portions providing the mechanical joint.

The invention will now be described with reference to the accompanying drawing, in which:

Fig. 1 is a longitudinal sectional view of a fluorescent lamp in accordance with the invention;

Fig. 2 is a plan view of the split tape.

Referring to Fig. 1, a fluorescent lamp according to the invention comprises a cylindrical discharge vessel I having a length, for example, of about 120 cms., and an The ends of the discharge vessel are closed in an airtight manner by conventional pinchings 2, 2 in which stap wires 3, 3 and 4, 4 of activated filament electrodes 5 and 6, respectively, are

housed. The inner side of the discharge vessel 1 is coated with a layer of fluorescing substances (not shown), and the discharge vessel is filled with a suitable gas, for example, argon under a pressure of a few mms. at room temperature and a small quantity of mercury in order to produce a low-pressure mercury vapor discharge during normal operation.

2,748,309 te ed May 2. 19 .5

T er s de of the discharge vessel s prov ded with a conductive layer in the form of a strip 7, which extends Substantially throughout the length of the discharge vessel.

This strip 7, which is made of a mixture of graphite and glaze, vand which has a resistance of 20 to 30 ohm/cm, is connected by means of a form-chromium tape ,8 and a short metal wire 9 to the lower stay wire 3 of the ;fil ament electrode 5.

The end of the metal tape 8 facing the strip 7 is divided by two cuts into three longitudinal portions 19, 11 and 12 (see Fig. 2). The central portion 11 is in direct electrical contact with the strip 7, whereas the outer longitudinal portions 10 and 12 are slightly bent upwards to form an arc (Fig. 1). The intermediate space between the arc formed by the outer portions 10 and 12 and the strip 7 or tube wall 1 is filled with an adhesive substance (not shown), which is made, for example, of a mixture of glass powder, graphite and a suitable binder, e. g. nitrocellulose or benzylcellulose.

The pinchings 2 are manufactured separately and in a subsequent stage they are sealed to the discharge vessel. The left-hand pinching is provided, prior to sealing, with the metal tape 8, which is welded to one of the stay wires 3 with the aid of the metal wire 9. Prior to the introduction of the left-hand pinching into the discharge vessel, the adhesive is applied, for example, by immersion, to the free end of the metal tape, which consists of the longitudinal portions 10, 11 and 12. The adhesive is then removed from the bottom side of the central portion 11 so that it sticks in the bent-up arc formed by the outer portions 10 and 12 and, possibly, to the top side of the central portion 11. During the introduction of the lefthand pinching, the clean bottom side of the longitudinal portion 11 slides along part of the strip 7 and makes contact therewith. During the sealing of the left-hand pinching to the discharge vessel, the adhesive is heated and thus becomes liquid and establishes a rigid mechanical connection between the outer portions 16 and 12, and the strip 7 and, probably, also part of the wall 1 of the discharge vessel. Due to this strong mechanical connection, a permanent satisfactory electrical connection is established between the blank bottom side of the portion 11 and the strip 7. y

The conducted strip 7 operates as an ignition electrode. Upon applying a suitable voltage between the activated main electrodes 5 and 6, a glow discharge is produced between the electrode 6, as a cathode, not connected to the strip, and the end of the strip 7 facing this electrode, this glow discharge travelling from the electrode 6 along the strip 7, the tape 8, the wire 9 and part of the lower stay wire 3 and finding its way finally to the electrode 5. As soon as the glow discharge has heated the electrodes 5 and 6 to emissive temperature, it is transformed into an arc discharge.

The embodiment relates to the electrical connection between an internal ignition stripand a main electrode of an electric discharge tube. However, it will be obvious that the invention may, for example, be used with advantage in high-vacuum tubes, the discharge vessel of which is coated internally with a conductive layer which requires an external electrical connection.

While we have thus described our invention with specific examples and embodiments thereof, other modifications will be readily apparent to those skilled in the art without departing from the spirit and the scope of the invention as defined in the appended claims.

What I claim is:

1. In an electric discharge tube comprising an insulating envelope, an electrode within said envelope, and a conductive layer on the inner surface of said envelope; a metal tape having one end electrically connected to said elec- 3 4 trode and the other end effecting electrical connection to 3. An electric discharge tube as set forth in claim 1 said conductive layer, said other end of said tape being wherein the metal tape is constituted of ferro-chromiurn, divided in the direction of its length forming at least two and the conductive layer is constituted of a graphiteadjacent portions, and adhesive means rigidly securing at ceramic mixture. least one of the adjacent portions to the conductive layer, 5 at least another of said adjacent portions being only in References Cit d i th fil f thi patent direct electrical contact engagement With the conductive layer and being free of said adhesive means. UNITED STATES PATENTS 2. An electric discharge tube as set forth in claim 1 2,291,965 .Tancke et al. Aug. 4, 1942 wherein said other end of the tape is divided into three 10 2,444,397 Cram June 29, 1948 adjacent portions, the adhesive means securing the outer 2,491,854 Force Dec. 20, 1949 two portions to the conductive layer. 2,663,823 Elenbaas et a1 Dec. 22, 1953 

